Method for manufacturing of three-dimensional freestanding porous thin-graphite with hierarchical porosity

ABSTRACT

The present invention includes an apparatus and a method of making a three dimensional graphite structure with a controlled porosity comprising: plating a metal layer on at least one of a nickel, an iron or a cobalt foam substrate; annealing the metal and the nickel, iron or cobalt foam into a porous metal-nickel, iron or cobalt catalyst, wherein the catalyst has a smooth and a porous surface; etching the smooth surface of the annealed porous metal-nickel, iron or cobalt catalyst; growing a carbonaceous layer on the porous surface of the annealed porous metal-nickel, iron or cobalt catalyst; and completely etching the porous metal-nickel, iron or cobalt catalyst to obtain the graphite layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Application Ser. No. 62/011,383 filed Jun. 12, 2014, which is incorporated herein by reference in its entirety.

STATEMENT OF FEDERALLY FUNDED RESEARCH

This invention was made with government support under Grant No. CMMI1150767 awarded by the National Science Foundation. The government has certain rights in the invention.

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to the field of three-dimensional manufacturing, and more particularly, to a novel method for manufacturing of three-dimensional freestanding porous thin-graphite with hierarchical porosity.

BACKGROUND OF THE INVENTION

Without limiting the scope of the invention, its background is described in connection with three-dimensional carbon-based structures.

The fast depletion of fossil energy and the associated adverse environmental impacts make it highly desirable to explore renewable-energy technologies. Carbonaceous materials with various morphologies and chemistries, such as carbon nanotubes¹⁻³, bucky balls^(4, 5), graphene⁶⁻⁸, and thin graphite⁹⁻¹², have emerged as key structures for energy storage and conversion devices¹³⁻¹⁷. Among them, thin graphite has received considerable interest as electrode supports owing to their high electric conductivity, excellent mechanical durability, and ultra-low mass density^(9, 18). However, it remains a challenge to rationally and efficiently synthesize carbonaceous materials into 3-D porous nanosuperstructures, which boast both high specific surface areas and fast ionic transports that significantly improve the performance of energy devices.

Previously, intensive research demonstrated the ultra-large specific surface area of graphene and its usage in energy devices, such as supercapacitors^(19, 20). Nevertheless, the assembly of graphene sheets is difficult to control, which could reduce the actual available surface areas and thus lower the device performance²¹. Recently, commercially available 3-D nickel foams were employed as catalysts for the synthesis of 3-D thin graphite²². Although this approach resolved the assembly problem of carbonaceous materials as electrodes for energy devices, the feature size of the as-obtained graphite resides at a scale of ˜100 μm. Complex chemical synthesis can produce porous carbon with pore sizes of a few nanometers²³. Nevertheless, it remains extremely difficult to achieve 3-D carbonaceous nanostructures with multilevel porosity, which promises high surface areas and enhanced ionic transport²⁴.

SUMMARY OF THE INVENTION

In one embodiment, the present invention includes a method of making a three dimensional graphite structure with a controlled porosity comprising: plating a metal layer on at least one of a nickel, an iron or a cobalt foam substrate; annealing the metal and the nickel, iron or cobalt foam into a porous metal-nickel, iron or cobalt catalyst, wherein the catalyst has a smooth surface and an embedded porous microstructure under the surface; etching the smooth surface of the annealed porous metal-nickel, iron or cobalt catalyst; the porous microstructures can be readily exposed, then growing a carbonaceous layer on the porous surfaces of the annealed metal-nickel, iron or cobalt catalyst; and completely etching the porous metal-nickel, iron or cobalt catalyst to obtain the graphite layer. In one aspect, the carbonaceous layer is graphene or graphite that is deposited on the annealed porous copper-nickel catalyst by at least one of chemical vapor deposition, plasma enhanced chemical vapor deposition or sputtering. In another aspect, the metal is a catalyst for graphene/graphite growth. In another aspect, the step of plating the metal is selected from at least one of electroplating or electroless plating. In another aspect, the metal is selected from at least one of copper, nickel, iron, cobalt, gold, platinum, or rhodium, but different from the foam material. In another aspect, the carbonaceous layer is deposited on the annealed porous copper-nickel catalyst by chemical vapor deposition in ethylene at between 600-700° C. In another aspect, the carbonaceous layer is graphite. In another aspect, the carbonaceous layer is freestanding and flexible. In another aspect, the conductivity of the graphite structure with 2 μm porosity is improved by 3 times when compared to that of the graphite structure without porosity. In another aspect, the further comprises the step of growing a metal hydroxide layer on the graphite layer. In another aspect, the method further comprising the step of growing at least one of a metal hydroxide, an oxide or a sulfide layer on the graphite layer, wherein the metal hydroxide/oxide/sulfide is selected from at least one of Ruthenium(IV) oxide; Aluminum hydroxide; Beryllium hydroxide; Cobalt(II) hydroxide; Cobalt oxide; Copper(II) hydroxide; Copper oxide; Curium hydroxide; Gold(III) hydroxide; Iron(II) hydroxide; Iron oxide; Mercury(II) hydroxide; Nickel(II) hydroxide; Nickel oxide; Nickel sulfide; Manganese oxide (MnO₂ or Mn₃O₄); Manganese sulfide; Tin(II) hydroxide; Tin(IV) Oxide; Uranyl hydroxide; Zinc hydroxide; Zirconium(IV) hydroxide; Gallium(III) hydroxide; Lead(II) hydroxide; or Thallium hydroxide. In another aspect, the carbonaceous layer is formed into an electrode support for metal hydroxide supercapacitors. In another aspect, the carbonaceous layer with a metal hydroxide/oxide/sulfide is formed into an electrode having a specific capacitance of at least 1149 F/g at a current density of 1.5 A/g. In another aspect, the carbonaceous layer with a metal hydroxide/oxide/sulfide is formed into an electrode having at least 97.5% capacitance retention after 4,000 cycles. In another aspect, the carbonaceous layer with a metal hydroxide/oxide/sulfide is formed into an electrode having at least 90% capacitance after 10,000 cycles. In another aspect, the method further comprises the step of adjusting the porosity of the nickel foam substrate to change the porosity of the graphite layer by at least one of controlling the copper deposition amount, annealing temperature, and annealing time. In another aspect, the step of etching the porous metal-nickel, iron or cobalt catalyst is defined further as selecting an etching agent that etches the annealed porous metal-nickel, iron or cobalt. In another aspect, the step of etching the porous metal-nickel, iron or cobalt catalyst is defined further as etching the copper-nickel catalyst in 1 M iron chloride (FeCl₃) and 2 M hydrochloride (HCl) at 50-80° C. overnight.

In another embodiment, the present invention includes a method of making an electrode from a three dimensional graphite structure with a controlled porosity comprising: annealing a metal and the nickel, iron or cobalt foam into a porous metal-nickel, iron or cobalt catalyst, wherein the catalyst has a smooth surface and an embedded porous microstructure under the surface; etching the smooth surface of the annealed porous metal-nickel, iron or cobalt catalyst; the porous microstructures can be readily exposed, then growing a carbonaceous layer on the porous surfaces of the annealed metal-nickel, iron or cobalt catalyst; and completely etching the porous metal-nickel, iron or cobalt catalyst to obtain the graphite layer; and growing at least one of a metal hydroxide, an oxide, or a sulfide layer on the graphite layer. In one aspect, the graphite is deposited on the annealed porous copper-nickel catalyst by at least one of chemical vapor deposition, plasma enhanced chemical vapor deposition or sputtering. In another aspect, the metal is a catalyst for graphene/graphite growth. In another aspect, the metal is at least one of copper, nickel, iron, cobalt, gold, platinum, or rhodium, but different from the foam material. In another aspect, the graphite is deposited on the annealed porous copper-nickel catalyst by chemical vapor deposition in ethylene at between 600-700° C. In another aspect, the graphite layer is freestanding and flexible. In another aspect, the conductivity of the graphite structure with 2 μm porosity is improved by 3 times when compared to that of a graphite structure without porosity. In another aspect, the graphite layer is formed into an electrode support for metal hydroxide supercapacitors. In another aspect, the at least one of metal hydroxide, oxide or sulfide layer is selected from at least one of Ruthenium(IV) oxide; Aluminum hydroxide; Beryllium hydroxide; Cobalt(II) hydroxide; Cobalt oxide; Copper(II) hydroxide; Copper oxide; Curium hydroxide; Gold(III) hydroxide; Iron(II) hydroxide; Iron oxide; Mercury(II) hydroxide; Nickel(II) hydroxide; Nickel oxide; Nickel sulfide; Manganese oxide (MnO₂ or Mn₃O₄); Manganese sulfide; Tin(II) hydroxide; Tin(IV) Oxide; Uranyl hydroxide; Zinc hydroxide; Zirconium(IV) hydroxide; Gallium(III) hydroxide; Lead(II) hydroxide; or Thallium hydroxide. In another aspect, the graphite layer with a metal hydroxide/oxide/sulfide is formed into an electrode having a specific capacitance of at least 1149 F/g at a current density of 1.5 A/g. In another aspect, the graphite layer with a metal hydroxide/oxide/sulfide is formed into an electrode having at least 97.5% capacitance retention after 4,000 cycles. In another aspect, the graphite layer with a metal hydroxide/oxide/sulfide is formed into an electrode having at least 90% capacitance after 10,000 cycles. In another aspect, the method further comprises the step of adjusting the porosity of the nickel foam substrate to change the porosity of the graphite layer by controlling at least one of the copper deposition amount, annealing temperature, and annealing time. In another aspect, the step of etching the copper-nickel catalyst is defined further as selecting an etching agent that etches the annealed porous noble metal-nickel, iron or cobalt. In another aspect, the step of etching the copper-nickel catalyst is defined further as etching the copper-nickel catalyst in 1 M iron chloride (FeCl₃) and 2 M hydrochloride (HCl) at 50-80° C. overnight.

Yet another embodiment of the present invention includes a three dimensional graphite structure with a controlled porosity made by a method comprising: electroplating a metal layer on at least one of a nickel, an iron or a cobalt foam substrate; annealing the metal and the nickel, iron or cobalt foam into a porous metal-nickel, iron or cobalt catalyst, wherein the catalyst has a smooth and a porous surface; etching the smooth surface of the annealed porous metal-nickel, iron or cobalt catalyst; growing a graphite layer on porous surface of the annealed porous metal-nickel, iron or cobalt catalyst; and completely etching the porous metal-nickel, iron or cobalt catalyst to obtain the graphite layer. In one aspect, the graphite is deposited on the annealed porous copper-nickel catalyst by at least one of chemical vapor deposition, plasma enhanced chemical vapor deposition or sputtering. In another aspect, the metal is a catalyst for graphene/graphite growth. In another aspect, the metal is copper, nickel, iron, cobalt, gold, platinum, or rhodium, but different from the foam material. In another aspect, the step of plating the metal is selected from at least one of electroplating or electroless plating. In another aspect, the graphite is deposited on the annealed porous copper-nickel catalyst by chemical vapor deposition in ethylene at between 600-700° C. In another aspect, the graphite layer is freestanding and flexible. In another aspect, the conductivity of the graphite structure with 2 μm porosity is improved by 3 times when compared to that of a graphite structure without porosity. In another aspect, the method further comprises the step of growing a metal hydroxide layer on the graphite layer. In another aspect, the method further comprises the step of growing at least one of a metal hydroxide, an oxide or a sulfide layer on the graphite layer, wherein the metal hydroxide/oxide/sulfide is selected from at least one of Ruthenium(IV) oxide; Aluminum hydroxide; Beryllium hydroxide; Cobalt(II) hydroxide; Cobalt oxide; Copper(II) hydroxide; Copper oxide; Curium hydroxide; Gold(III) hydroxide; Iron(II) hydroxide; Iron oxide; Mercury(II) hydroxide; Nickel(II) hydroxide; Nickel oxide; Nickel sulfide; Manganese oxide (MnO₂ or Mn₃O₄); Manganese sulfide; Tin(II) hydroxide; Tin(IV) Oxide; Uranyl hydroxide; Zinc hydroxide; Zirconium(IV) hydroxide; Gallium(III) hydroxide; Lead(II) hydroxide; or Thallium hydroxide. In another aspect, the graphite layer is formed into an electrode support for metal hydroxide supercapacitors. In another aspect, the graphite layer with a metal hydroxide/oxide/sulfide is formed into an electrode having a specific capacitance of at least 1149 F/g at a current density of 1.5 A/g. In another aspect, the graphite layer with a metal hydroxide/oxide/sulfide is formed into an electrode having at least 97.5% capacitance retention after 4,000 cycles. In another aspect, the graphite layer with a metal hydroxide/oxide/sulfide is formed into an electrode having at least 90% capacitance after 10,000 cycles. In another aspect, the method further comprises the step of adjusting the porosity of the nickel foam substrate to change the porosity of the graphite layer by controlling at least one of the copper deposition amount, annealing temperature, and annealing time. In another aspect, the step of etching the copper-nickel catalyst is defined further as selecting an etching agent that etches the annealed porous noble metal-nickel, iron or cobalt. In another aspect, the step of etching the copper-nickel catalyst is defined further as etching the copper-nickel catalyst in 1 M iron chloride (FeCl₃) and 2 M hydrochloride (HCl) at 50-80° C. overnight.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures and in which:

FIGS. 1A to 1D, the procedure for porosifying Ni—Cu catalysts, (FIGS. 1E-1F) 3-D porous thin graphite, and (FIG. 1G) growth of Ni(OH)₂ on porous graphite. FIG. 1H are optical images of Ni foam, porous thin graphite, and porous graphite/Ni(OH)₂. FIG. 1I is an Scanning Electron Microscope (SEM) image and Energy Dispersive Spectroscopy (EDS) mappings of the cross-section of Cu—Ni foam after annealing at 1000° C. using the method taught in FIGS. 1A to 1G.

FIGS. 2A to 2H show: (FIG. 2A) SEM images of the original Ni foam, (FIG. 2B-2D) porosified foams made of Ni/Cu alloys, and (FIG. 2E) multilevel porous thin graphite, (FIG. 2F) Tunneling Electron Microscope (TEM) images of the cross-sections of multilevel porous graphite (Insets: Fast Fourier Transform (FFT) and High Resolution Tunneling Electron Microscope (HRTEM) image), and (FIG. 2G) SEM image of porous graphite/Ni(OH)₂, (FIG. 2H) morphology of Ni(OH)₂ grown on the multilevel porous graphite (Inset: sideview of graphite/Ni(OH)₂ shows the thickness of Ni(OH)₂ nanoplates). FIG. 2I are an SEM images and EDS mappings of the cross-sections and surfaces of porous Cu—Ni catalysts after electrochemical etching.

FIGS. 3A to 3B show: (FIG. 3A) Raman spectrum of the as-obtained multilevel porous graphite and (FIG. 3B) the XRD of Ni(OH)₂ on the porous graphite.

FIGS. 4A to 4F show: (FIG. 4A, FIG. 4B) Cyclic voltammograms and galvanostatic discharging curves of porous graphite/Ni(OH)₂ electrodes in 3M KOH aqueous solution; (FIG. 4C) Specific capacitance of porous graphite/Ni(OH)₂ at various scan rates and discharge currents and (FIG. 4D) the specific capacity at various discharge currents based on the mass of the entire graphite/Ni(OH)₂ electrodes; (FIG. 4E) Nyquist plots of the porous graphite/Ni(OH)₂; (FIG. 4F) Cycling performance measured at a current density of 20 A/g in a potential range of 0 to 0.5 V. FIGS. 4G-A and 4G-B are cyclic voltammogram and galvanostatic discharging curves of Ni(OH)₂ on the non-porous 3-D graphite. FIGS. 4H-A to 4H-D are SEM images of Ni(OH)₂ nanostructures on the non-porous 3-D graphite. FIG. 4I is a photo of flexible porous graphite/Ni(OH)₂.

FIGS. 5A and 5B show: (FIG. 5A) Raman spectrum of thin graphite with two-level porosity and (FIG. 5B) XRD of Mn₃O₄ grown on such a support.

FIGS. 6A to 6F show: SEM images of Mn₃O₄ grown on 3-D thin graphite with two-level porosity for (FIGS. 6A-6C) 20 minutes and (FIGS. 6D-6F) 30 minutes, respectively.

FIGS. 7A to 7F show: SEM images of Mn₃O₄ grown on simple 3-D thin graphite with one level of porosity of ˜100 μm for (FIGS. 7A-7C) 20 minutes and (FIGS. 7D-7F) 30 minutes, respectively. GMSP: the graphite/Mn₃O₄ with single-level porosity.

FIGS. 8A to 8D show: (FIG. 8A) CV curves of the graphite/Mn₃O₄ with multilevel porosity (GMMP-20) at scanning rates from 1 to 200 mV/s. (FIG. 8B) Charging-discharging curves of the graphite/Mn₃O₄ with multilevel porosity (GMMP-20) from 1 to 10 A/g. (FIG. 8C) Nyquist plots of the graphite/Mn₃O₄ with multilevel porosity (GMMP-30) and (GMMP-20), (FIG. 8D) capacitive retention as a function of cycle numbers of the GMMP-30 at a current density of 10 A/g.

FIG. 9 shows an as-synthesized 3-D thin graphite with a single-level of porosity (100 μm in feature size) directly from the Ni foams.

FIGS. 10A and 10B, show (FIG. 10A) CV curves of the graphite/Mn₃O₄ with single-level porosity (GMSP-30) at scanning rates from 1 to 200 mV/s. (FIG. 10B) Charging-discharging curves of the graphite/Mn₃O₄ with single-level porosity (GMSP-30) from 1 to 10 A/g.

FIGS. 11A to 11I show: (FIGS. 11A-11C) sizes dependence of porosity on the Cu deposition amount, annealing temperature and annealing time, respectively; (FIG. 11D-11E), (FIGS. 11F-11G), (FIGS. 11H-11I) SEM images of Cu—Ni alloy foam with second level of porosity of ˜2 μm, 5 μm, and 8 μm, respectively. (The scales bar in 11D, 11F, 11H are 20 μm and in 11E, 11G, 11I are 100 μm)

FIGS. 12A to 12G show: (FIG. 12A-12B), (FIG. 12C-12D), (FIG. 12E-12F) multilevel porous thin graphite with second level of porosity of ˜2 μm, 5 μm, and 8 μm, respectively. (The scales bar in 12A, 12C, 12E are 20 μm and in 12B, 12D, 12F are 50 μm) (12G) the conductivity of multilevel porous thin graphite and single-level porous thin graphite at different densities.

DETAILED DESCRIPTION OF THE INVENTION

While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention.

To facilitate the understanding of this invention, a number of terms are defined below. Terms defined herein have meanings as commonly understood by a person of ordinary skill in the areas relevant to the present invention. Terms such as “a”, “an” and “the” are not intended to refer to only a singular entity, but include the general class of which a specific example may be used for illustration. The terminology herein is used to describe specific embodiments of the invention, but their usage does not delimit the invention, except as outlined in the claims.

As used herein, a “carbonaceous layer” may be formed from a variety of known carbonaceous materials, such as graphene, graphite, activated carbon, carbon black, or carbon containing structures or polymers that can be used for electronic devices, e.g., capacitors.

The present inventors describe herein an innovative mechanism for the synthesis of three-dimensional (3-D) thin-graphite superstructures with a controlled porosity from engineered catalysts and their applications in electrochemical supercapacitors. The 3-D thin-graphite nanostructures with two levels of porosity were synthesized by using porous nickel-copper (Ni—Cu) catalysts-engineered from Ni foams by an electrodeposition/etching process. The as-grown graphite is 3-D, multilevel porous, freestanding, and flexible after selective etching of the catalysts. Thin nickel hydroxide nanoplates [Ni(OH)₂] and manganese (II, III) oxide (Mn₃O₄) were grown on the 3-D graphite nanosuperstructures. The electrochemical tests showed a specific capacitance of ˜1149 F/g (or 137 mAh/g in specific capacity) at a current density of 1.5 A/g, based on the entire weight of the graphite/Ni(OH)₂ electrodes. The devices also exhibit excellent cyclibility compared to previous work, with 97.5% retention after 4,000 cycles. The high performance of the device was attributed to the unique features of the as-synthesized porous graphite/Ni(OH)₂ electrodes. The graphite coated with Mn₃O₄ nanocrystals was demonstrated as electrodes for supercapacitors as well, which offers an ultrahigh specific capacitance of 407 F/g at 1 mV/s (or 399 F/g at 1 A/g), based on the total weight of the electrodes. It was also found that these devices also exhibit surprisingly long cycle stability with capacitance retentions of 99.5% and 90% after 2,500 and 10,000 charge-discharge cycles, respectively, at a rate of 10 A/g. The innovative mechanism for the synthesis of 3-D porous graphite is efficient, controllable, and has a low cost, which may potentially spur a new paradigm for manufacturing 3-D porous graphene/graphite materials for an array of energy storage and conversion applications.

The present invention includes a novel synthetic method and devices made therewith for large-scale thin graphite nanosuperstructures with multilevel porosity. The graphite was grown by Chemical Vapor Deposition (CVD) on 3-D porous Ni—Cu alloys, which were strategically engineered from the commercial Ni foams via an alloying-selective-etching process. The as-grown graphite was 3-D and freestanding with two levels of porosity of ˜100 μm and less than 10 μm, respectively. The second level of porosity could be tuned from 2 μm to 8 μm by controlling the Cu deposition amount, annealing temperature or annealing time. It is demonstrated herein that this material as supports for nickel hydroxide [Ni(OH)₂] energy storage devices. A specific capacitance ˜1149 F/g (or 137 mAh/g in specific capacity) was obtained at a current density of 1.5 A/g, based on the mass of the entire electrode of graphite/Ni(OH)₂. This value is among the highest of the state-of-the-art Ni(OH)₂ supercapacitor devices. Moreover, the porous graphite/Ni(OH)₂ exhibits excellent stability, with 97.5% specific capacitance retained after 4,000 charging-discharging cycles. We attribute these enhanced performances to the large specific surface area, excellent crystallinity, and high assembling quality of the 3-D porous graphite/Ni(OH)₂. A specific capacitance of 407 F/g at 1 mV/s (or 399 F/g at 1 A/g) was achieved based on the total mass of the porous graphite/Mn₃O₄(GMMP) electrode. The GMMP exhibits long cycle stability, with 99.5% and 90% specific capacitance retained after 2,500 and 10,000 charging-discharging cycles, respectively. Thus, the present inventors provide a new paradigm for manufacturing 3-D carbonaceous nanosuperstructures for a number of energy-storage-and-conversion devices.

In one example, a 3-D porous graphite was catalyzed from a 3-D porous Cu—Ni superstructure, which was obtained by strategically porosifying commercially available 3-D Ni foams (10) via an alloying-etching approach [FIGS. 1A to 1G]. The approach includes three steps: firstly, an alloying element, in this example Cu, which was conformably coated (12) on the entire surface of 3-D Ni foams (10) by electrodeposition at −0.8 V (v.s. Ag/AgCl) for, e.g., 100 minutes from an electrolyte made of 2M CuSO₄.5H₂O, and 1 M HBO₃ FIGS. 1A-1B). The Cu thin films were deposited on all interconnected branches of the 3-D Ni foam with a thickness of approximately 5 μm. Next, the Cu—Ni composite was annealed (14) at a temperature of 1000° C. for interfacial atomic diffusion and alloying for 1 hour in Argon gas before cooled to the room temperature [FIG. 1C]. Energy-dispersive X-ray spectroscopy (EDX) showed that Cu is uniformly alloyed with Ni [FIG. 1I], as Cu is a material that is completely miscible with Ni²⁵. Next, the Cu—Ni alloy foam was etched electrochemically at 0.6 V (v.s. Ag/AgCl) for 1000 sec, which resulted in arrays of micropores of ˜5 μm on the 3-D surfaces of Cu—Ni foams [FIG. 1D and FIG. 2B]. Now, the feature size of the Ni foam was reduced from ˜100 μm to 5 μm [FIGS. 2A-2D], an order of magnitude reduction. Cross-sectional SEM images revealed that more than two-thirds surfaces of Ni foams are porosified [FIG. 2C]. Brunauer-Emmett-Teller (BET) surface area characterization determined approximately 2-time increment of the total surface area from 5.3×10⁻² m²/cm³ to 9.6×10⁻² m²/cm³. The as-synthesized porous foams contained both Cu and Ni as shown in the EDX characterization [FIG. 2I]. The pore morphology and size could be readily tuned from 2 μm to 8 μm by the Cu deposition amount, annealing time, and annealing temperature [FIGS. 11D-11I]: the more Cu is deposited on the Ni foam, the larger the pore size is [FIG. 11A]; both the longer annealing time and the higher annealing temperature could also lead to lager pore size [FIGS. 11B-11C]. The pore density could also be controlled by the etching rate and etching time. The pore formation mechanism will be investigated and reported elsewhere.

Next, employing such 3-D porous Cu—Ni template, graphite (16) can be readily grown via a low-temperature chemical-vapor-deposition process followed by selective etching of the porous Cu—Ni catalysts [FIGS. 1A-1F]. A piece of porous Cu—Ni superstructure was loaded into the stable heating zone of a tube furnace. A mixture of argon (Ar)/hydrogen (H₂) was flushed into the furnace at a rate 20 sccm and 0.15 torr for 0.5 hour. Then the reaction temperature was increased to 600° C. in the presence of Ar/H₂ before ethylene was introduced at 20 sccm for 30 minutes. Next, the sample was rapidly cooled to the room temperature. Next, the Cu—Ni alloy was etched in 1 M iron chloride (FeCl₃) and 2 M hydrochloride (HCl) at 50-80° C. overnight, freestanding thin-graphite superstructures 18 with two-levels of porosity of ˜100 and <10 μm were readily obtained [FIG. 1F and FIG. 2E]. The pores showed smoother features than that of the Cu—Ni template. The pore size is essentially the same as that of Cu—Ni alloy foam, approximately 5 μm here [FIG. 2D]. Note that the pore size of thin-graphite could also be tuned from 2 μm to 8 μm as the Cu—Ni alloy foam [FIGS. 12A-12F]. The conductivity of the 3-D porous multilevel porous graphite is significantly improved than the non-porous graphite and depends on the pore size [FIG. 12G], shown here with a Ni(OH)s layer (20) that is grown on the graphite (18). The lattice fringe in HRTEM [FIG. 2F], the small D band in Raman spectrum [FIG. 3A], and clear diffraction peaks in XRD [FIG. 3B] suggest the high crystallinity of graphite in spite of the low synthetic temperature of 600° C. Note that the symmetrical 2D peak and the high intensity ratio of the G and 2D peaks (>1) of the Raman spectrum further confirmed the as-synthesized material is graphite.

Previously, graphene/thin graphite materials were largely synthesized on Cu²⁶, Ni^(27, 28) or Cu—Ni substrates²⁹ in methane at 900˜1050° C.³⁰. The use of ethylene can decrease the required temperature to 750° C.³¹, due to a lower dissociating energy required for ethylene. Here, a highly crystalline graphite was obtained at only 600° C., which could be attributed to the higher catalytic activity of Cu—Ni alloys than those of pure Cu or Ni³². This low-temperature CVD method is indeed desirable for preserving the fine porous structures of the Cu—Ni alloys for growing graphite.

Moreover, the 3-D porous graphite is flexible and mechanically self-supportive [FIG. 4I and FIG. 1H]. After loaded with energy materials, such as Ni(OH)₂ [FIG. 1H], they can be directly applied as electrodes without use of the bonding agents. Note that the bonding agents can reinforce electrodes, but often adversely increase the total weight and decrease the electric conductance of the electrodes. As a result, the mechanical self-supportiveness along with the high electric conductivity and low mass density make the 3-D porous thin-graphite a good candidate for electrochemical energy storage devices.

The present inventors demonstrate herein a multilevel porous graphite superstructure for Ni(OH)₂ energy storage devices. Ni(OH)₂ is an well-known material for rechargeable alkaline batteries, which is also considered as pseudocapacitive for electrochemical capacitors³³⁻³⁶. The present inventors developed a method for the synthesis of Ni(OH)₂ electrodes that differs from those in a previous report²². First, a porous graphite was treated in 4 M nitric acid (HNO₃) at 50° C. for 2 hour to increase the surface hydrophilicity. Then, the material was immersed in a solution mixture of nickel chloride (NiCl₂, 7 mM) and urea (40 mM) at 180° C. for 2 hours. The reaction resulted in arrays of hexagonal nanoplates, conformably coated on the entire surface of the porous graphite, with side lengths of ˜250 nm and thickness of tens of nanometers [FIGS. 2G-2H]. It was determined as crystalline Ni(OH)₂ by XRD measurements [FIG. 3B]. The structure of porous graphite/Ni(OH)₂ has an excellent electric conductivity as shown in the Nyquist plot of electrochemical impedance spectrum (EIS), where the equivalent series resistance (ESR) was only 0.8Ω [FIG. 4E].

The electrochemical performance of the porous graphite/Ni(OH)₂ was tested in a three-electrode cell setup in a potassium hydroxide solution (KOH, 3 M) with Ag/AgCl and Platinum (Pt) as the reference and counter electrodes, respectively. The performances were analyzed by the cyclic voltammetry (CV) and galvanostatic charge-discharge characterizations. FIG. 4A shows the CV curves at scanning rates from 1-15 mV/sec (0-0.6 V v.s. Ag/AgCl). Different from those nearly rectangular CV curves observed in electric double-layer capacitors, the CV tests of Ni(OH)₂/graphite showed two redox peaks, like those of batteries³⁷. It is due to the Faradaic redox reactions, often observed on pesudocapacitive materials. The reaction is given as³⁸.

Ni(OH)₂+OH⁻⇔NiOOH+H₂O+e ⁻.

With the increase of the scan rate, the shapes of the CV curves systematically altered, where the potential of both the anodic and cathodic peaks shifted to the positive and negative potentials, respectively. This effect could be attributed to the slower ion diffusion and less complete redox reactions at higher scanning rates^(39, 40). The specific capacitance (C) can be calculated from C=∫IdV/(νmV), where I is the electric current, ν is the potential scan rate, m is the mass of the electrode materials, and V is the potential window. The specific capacitance of the porous graphite/Ni(OH)₂ composite was determined as 3125 F/g and 906 F/g (2 mV/s) based on the weight of Ni(OH)₂ and the total mass of the porous graphite/Ni(OH)₂ electrode, respectively [FIG. 4C]. The value of 3125 F/g calculated from the mass of Ni(OH)₂ is among the highest reported for Ni(OH)₂ capacitors⁴¹. The specific capacitance was also obtained from the galvanostatic-discharge measurements (FIG. 4B), given by C=(IΔt)/(mΔV), where I, Δt, m, and ΔV are the discharging current, time, mass of the electrode material, and potential change, respectively. Note that there is a plateau in the discharging curve, which resembles the behavior of batteries³⁷. The as-measured specific capacitance reduced with the increase of discharging current (FIG. 4C). A specific capacitance of ˜3962 F/g and 1149 F/g was obtained at 1.5 A/g based on the mass of Ni(OH)₂ and the total mass of porous graphite/Ni(OH)₂, respectively (FIG. 4C). These values are close to those obtained from the CV measurement at a scanning rate of 2 mV/sec. It was found that the specific capacitance decreases with the scanning or discharging rate from 1149 at 1.5 A/g to ˜580 F/g at 12 A/g based on the entire mass of the electrode. However, even at the higher discharging rate, the value of ˜580 F/g (12 A/g) is still a few times higher than a recent report of 111 F/g obtained at a similar discharging rate (10 A/g)²². As previously mentioned, the Ni(OH)₂ behaviors like a battery. The specific capacity at different discharging rates [FIG. 4D] was determined. Capacities of 480 mAg/h and 137 mAh/g can be obtained at 1.5 A/g based on the mass of Ni(OH)₂ and the entire mass of the Ni(OH)₂/graphite electrode, respectively. The electrodes also exhibit good cyclic stability, where the specific capacitance reduced by 2.5% after 4,000 consecutive charge-discharge cycles at a current density of 20 A/g (FIG. 4F). In comparison, most previous work showed a few percentage of capacitance reduction after only 1,000-2,000 cycles⁴²⁻⁴⁴. Overall, the specific capacitance, capacity, and cyclibility of the Ni(OH)₂/graphite electrodes are surprisingly effective when compared to the recent reports as shown in Table 1.

TABLE 1 Comparison of electrochemical measurements in recent publications of Ni(OH)₂ supereapacitor electrodes and the present invention. Specific capacity: Specific Ni(OH)₂/* capacitance: with Ni(OH)₂/*with graphene/** Supporting graphene/**total total Materials electrode electrode and (current (mAh/g) testing density/scan Capacitance (Discharging Year Materials Additives conditions rate) retention rate) 2014¹ Graphite HPMC-10 wt % Ni Foam 1956 F/g 70% ~278 Ni(OH)₂ 6M KOH *N/A 1000 cycles *N/A nanosheet 0-1 V **N/A (10 A/g) **N/A (Hg/HgO) (1 A/g) (1 A/g) 2013² graphite NA Ni Foam ~1560 F/g 65% ~207 Ni(OH)₂ 6M KOH *N/A 1000 cycles *N/A Film 0-0.5 V **~166 F/g (10 A/g) **~22 (Ag/AgCl) (0.5 A/g) (1 A/g) 2013³ graphite AC- Ni Foam ~2188 F/g 97% N/A Ni(OH)₂ 80 wt % 1M KOH *N/A 1000 cycles *N/A film PVDF- 0-0.5 V **N/A 76% **N/A 10 wt % (Ag/AgCl) (1 mV/s) 10000 cycles AB- (100 mV/s) 10 wt % 2013⁴ GrapheneNi(OH)₂ PTFE- Platinum N/A ~95% ~ N/A flim 60 wt % foil *1327 F/g 2000 cycles *~156 hydrogel 6M KOH **N/A (16 A/g) **N/A 0-0.5 V (2 A/g) (2 A/g) (Ag/AgCl) 2012⁵ graphite AM-75% Ni Foam 1735 F/g N/A N/A Ni(OH)₂ PTFE-5% 6M KOH *N/A *N/A film AB-20% 0-0.5 V **N/A **N/A (Hg/HgO) (1 mV/s) 2012⁶ graphite AM-75% Ni Foam 2194 F/g 95.7% N/A Ni(OH)₂ PTFE-5% 6M KOH *N/A 2000 cycles *N/A nanosheet AB-20% −0.1-0.45 V **N/A (100 mV/s) **N/A (SCE) (2 mV/s) 2011⁷ Ni foam No Ni Foam 2675 F/g >96% N/A Ni(OH)₂ additive 1M NaOH *No graphite 500 cycles *No graphite nanowall 0-0.55 V **~7 F/g (30 mV/cm²) **~24 (SCE) (5 mV/cm²) (5 mV/cm²) 2010⁸ graphene PTFE-1% Ni Foam 1335 F/g ~100% ~250 Ni(OH)₂ 3% KOH *~935 F/g 2000 cycles *~170 nanosheet 0-0.5 V **N/A (28.6 A/g) **N/A (Ag/AgCl) (2.8 A/g) (2.8 A/g) 2008⁹ Ni foam No Ni Foam 3125 F/g ~48% ~444 Ni(OH)₂ additive 1M NaOH *No graphite 300 cycles *No graphite nanosheet −0.05-0.55 V **~39 F/g (4 A/g) **~6 (SCE) (4 A/g) (4 A/g) This Porous No Self 3125 F/g (2 mV/s) 97.5% 480 work graphite/ additive supported *1149 F/g 4,000 cycles *137 Ni(OH)₂ 1M KOH **1149 F/g (20 A/g) **137 sheet 0-0.6 V (1.5 A/g) (1.5 A/g) (Ag/AgCl)

Footnotes: Commercial available substrates were used. The density of commercially available 1.6 mm thick Ni foams and 0.1 mm Ti foil s are ˜40 mg/cm² and ˜45 mg/cm², respectively. All the parameters in the table have been given on the base of the three-electrode systems. (PTFE: poly(tetrafluoroethylene; AM: active materials; AB: acetylene black or carbon black; PVDF: polyvinylidene difluoride.) Table references:

-   1. Zhang, J. T.; Liu, S.; Pan, G. L.; Li, G. R.; Gao, X. P. Journal     of Materials Chemistry A 2014, 2, 1524-1529. -   2. Ji, J. Y.; Zhang, L. L.; Ji, H. X.; Li, Y.; Zhao, X.; Bai, X.;     Fan, X. B.; Zhang, F. B.; Ruoff, R. S. Acs Nano 2013, 7, (7),     6237-6243. -   3. Li, H. B.; Yu, M. H.; Wang, F. X.; Liu, P.; Liang, Y.; Xiao, J.;     Wang, C. X.; Tong, Y. X.; Yang, G. W. Nat Commun 2013, 4. -   4. Xu, Y. X.; Huang, X. Q.; Lin, Z. Y.; Zhong, X.; Huang, Y.;     Duan, X. F. Nano Res 2013, 6, (1), 65-76. -   5. Yan, J.; Fan, Z. J.; Sun, W.; Ning, G. Q.; Wei, T.; Zhang, Q.;     Zhang, R. F.; Zhi, L. J.; Wei, F. Adv Funct Mater 2012, 22, (12),     2632-2641. -   6. Yan, J.; Sun, W.; Wei, T.; Zhang, Q.; Fan, Z. J.; Wei, F. J Mater     Chem 2012, 22, (23), 11494-11502. -   7. Lu, Z. Y.; Chang, Z.; Zhu, W.; Sun, X. M. Chem Commun 2011, 47,     (34), 9651-9653. -   8. Wang, H. L.; Casalongue, H. S.; Liang, Y. Y.; Dai, H. J. J Am     Chem Soc 2010, 132, (21), 7472-7477. -   9. Yang, G. W.; Xu, C. L.; Li, H. L. Chem Commun 2008, (48),     6537-6539.

It was also important to compare the performance of the Ni(OH)₂/porous graphite with Ni(OH)₂/non-porous graphite. A control sample of Ni(OH)₂ grown on the non-porous thin graphite (obtained from non-porosified Ni foams) showed inferior electrochemical performances (FIGS. 4G-A-FIG. 4G-B and FIGS. 4H-A-4H-D). The specific capacitance was 231 F/g at 1 A/g (based on the total mass of the electrode) (FIGS. 4H-A-4H-D). This result is close to that reported previously but using a more simple and straightforward method²². It was found that, in the previous work, polymer binders were added to improve the mechanical strength of the electrodes, which are not necessary for use with the present invention. If the actual weight of polymer binders was included towards the total weight of the electrode, the specific capacitance could be much lowered to 12-38 F/g²². As a result, both the control experiments and previous work support the substantial enhancement of the energy material of Ni(OH)₂ by using the 3-D multilevel porous thin graphite made using the method of the present invention.

Mn₃O₄ is an also advantageous pseudocapacitive material with low cost, environmental compatibility, and large capacity⁴⁵. The synthesis began with the treatment of porous graphite in a nitric acid solution (HNO₃, 4 M) at 50° C. for 2 hours to increase the surface hydrophilicity. Next, a piece of thin graphite was immersed in a 30 mL autoclave containing a solution mixture made of potassium permanganate (KMnO₄, 0.1 mol/L) and sodium nitrite (0.1 mol/L NaNO₃). The reaction was kept at 150° C. for 20 to 30 minutes. The temperature was reduced to the room temperature naturally and the porous graphite/Mn₃O₄ nanosuperstructures were obtained after washing by D.I. water and drying in air. A series of graphite-Mn₃O₄ samples were synthesized in this manner by varying the reaction time and the growth substrates. The testing samples include graphite/Mn₃O₄ with multi-level porosity reacted for 20 minutes (GMMP-20, FIGS. 6A-6C) and 30 minutes (GMMP-30, FIGS. 6D-6F), respectively, graphite/Mn₃O₄ with single-level porosity reacted for 20 minutes (GMSP-20, FIGS. 7A-7C) and 30 minutes (GMSP-30, FIGS. 7D-7F), respectively. Here the samples of graphite/Mn₃O₄ with single-level of porosity were fabricated for control experiments.

For as-fabricated graphite/Mn₃O₄ nanostructures, the XRD diffraction patterns confirm the high crystallinity of both graphite and Mn₃O₄[Raman Shift FIG. 5A and FIG. 5B]. The 3-D thin graphite/Mn₃O₄ with multilevel porosities, including GMMP-20 [FIG. 6C], have Mn₃O₄ nanocrystals distributed on the surfaces of the thin graphite essentially uniformly with a size of 10-20 nm. The Mn₃O₄[FIG. 6C] nanocrystals obtained after reactions for 20 minutes (GMMP-20) exhibited a ˜32% in surface coverage. For the control samples, similar Mn₃O₄ nanocrystals were synthesized on the single-level porous graphite after reaction for 20 min [GMSP-20, FIG. 7A]. When the reaction time was increased to 30 minutes, the morphology of Mn₃O₄ was changed to nanosheets [GMMP-30, FIG. 7D]. This change could be attributed to the longer reaction time and the smaller available surface area, resulting in coalescence and transformation of nanoparticles.

Characterization of the electrochemical supercapacitive performance of the GMMP and the control samples of GMSP were carried out by cyclic voltammetry and galvanostatic charging-discharging of half-cells. A three-electrode cell setup was used with Graphite/Mn₃O₄ as the working electrode, Ag/AgCl as the reference electrode, platinum (Pt) serving and counter electrode, and potassium hydroxide (Na₂SO₄) solutions (1 M) as the electrolyte. From the CV measurement results, with increment of the scanning rates, the CV curves systematically deviated while remained symmetrically, which could be due to the incomplete electrochemical reactions at higher scan rates. The specific electrochemical capacitance (C) can be calculated from C=∫IdV/(νmV), where I is the electric current, ν is the potential scan rate, in is the mass of the electrode materials, and V is the potential window. The highest specific capacitance was obtained from GMMP-20 with a value of ˜407 F/g at 1 mV/s, based on the total weight of the electrode. This value is much higher than those found from GMSP-30 (201 F/g) (FIGS. 10A and 10B) obtained at the same scanning rate.

As shown in FIG. 9, a synthesized 3-D thin graphite with a single-level of porosity (100 μm in feature size) directly from the Ni foams. FIGS. 10A and 10B, compared to or GMSP-30 (˜201 F/g), GMMP-20 samples were fabricated on a substrate with 4-time larger specific surface areas (per unit mass) due to the presence of two levels of porosity and less mass per unit area. A specific capacitance as high as ˜407 F/g was achieved.

To further confirm the results obtained from the CV measurement, the present inventors determined the specific capacitance by using the galvanostatic charging-discharging characterization as shown in FIG. 6C. The highest specific capacitance of ˜399 F/g, based on the total weight of the electrode, such a value is close to that obtained from the CV measurement. These values are consistently higher than those reported recently of 107, 88, and 85 F/g at 2, 5, and 10 A/g, respectively⁴⁵.

FIGS. 8A to 8D show: (FIG. 8A) CV curves of the graphite/Mn₃O₄ with multilevel porosity (GMMP-20) at scanning rates from 1 to 200 mV/s. (FIG. 8B) Charging-discharging curves of the graphite/Mn₃O₄ with multilevel porosity (GMMP-20) from 1 to 10 A/g. The porous graphite/Mn₃O₄ with two levels of porosity (GMMP-30, GMMP-20) has high electric conductivity, as measured by the electrochemical impedance spectroscopy (EIS) (100 kHz to 0.01 Hz, FIG. 8C). The Nyquist plots of GMMP-30 and GMMP-20 show features with an arc and a spike at a high and a low frequency regime, respectively. Fitted with the equivalent circuit diagram [inset of FIG. 8C], the electrolyte resistance (Rs), charge transfer resistance (Rct), double layer capacitance (Cp), and the constant phase element (C_(PE)) for the redox reaction of Mn₃O₄ can be readily determined. The GMMP-30 and GMMP-20 exhibited small equivalent series resistances.

In addition to the ultrahigh specific capacitance as demonstrated above, the 3D freestanding graphite/Mn₃O₄ with multilevel porosity also showed superb long-term cycle stability. At a current density of 10 A/g, the charge-discharge cycling showed capacitance-retentions of 99.5% and 90% after 2500 and 10000 sequential cycles, respectively (FIG. 8D), which could be attributed to the mechanical and chemical robustness of the porous graphite/Mn₃O₄.

What contributes to the high performances of porous graphite/Ni(OH)₂ as well as the graphite/Mn₃O₄. By way of explanation, and in no way a limitation of the present invention, using porous graphite/Ni(OH)₂ as an example and ascribe it to three factors: first, although Ni(OH)₂ was synthesized at the same reaction conditions, the morphology of Ni(OH)₂ nanostructures on porous graphite are distinct from those grown on 3-D non-porous graphite in control experiments herein and the previous report²². The Ni(OH)₂ nanoplates uniformly and tightly grew on the porous graphite. The coating is conformable with an overall thickness estimated as ˜25 nm (FIG. 2H inset). While, for the non-porous graphite, flower-like Ni(OH)₂ with thickness of ˜150 nm were grown relatively loosely on graphite (FIG. 4I). The increased thickness and less well defined attachment of Ni(OH)₂ can result in higher total weight of Ni(OH)₂ and less effective charge storage in Ni(OH)₂. Second, the multilevel porous graphite offers a specific surface area with at least four time improvement than that of the 3-D graphite made in the control experiment, with ˜2 time increase in surface area and ˜2 time reduction in the total weight of the same sample volume. Moreover, no additive is necessary for the porous graphite electrodes of the present invention, which further reduced the total weight of the electrodes.²² As a result, a much higher specific capacitance could can be obtained due to the larger specific areas of the multilevel porous graphite/Ni(OH)₂. Third, the substantially enhanced specific area can result in more facile ionic transport⁴⁶. It also directly increased the electric double-layer capacitance⁴⁷, which also contributed to the measured total specific capacitance.

In summary, the present invention includes a novel approach for the synthesis of 3-D multilevel porous graphite superstructures using engineered porous Cu—Ni alloys as catalysts. The graphite superstructures were applied as supports for Ni(OH)₂ energy storage devices, which offer a specific capacitance of ˜1149 F/g at a current densities of 1.5 A/g (or 137 mAh/g in specific capacity), based on the entire mass of graphite/Ni(OH)₂ electrode. The devices also exhibit excellent cyclibility with 97.5% capacitance retention after 4,000 cycles. The performances are among the best reported previously. The high specific capacitance and long durability of the supercapacitors could be attributed to the high specific surface area, excellent crystalline quality, controlled 3-D assembly of Ni(OH)₂, and good electric conductivity. The 3-D porous graphite/Ni(OH)₂ composites are also advantageously flexible and self-supportive, which can be directly applied as electrodes without binders or additives. The graphite coated with Mn₃O₄ nanocrystals was demonstrated as electrode for supercapacitors. It offered a specific capacitance as high as 407 F/g at 1 mV/s and 399 F/g at 1 A/g, based on the total weight of the electrodes. The devices also exhibit long cycle stability with capacitance retentions of 99.5% after 2,500 charge-discharge cycles and 90% after 10,000 cycles at a current of 10 A/g. Overall, the reported mechanism for the synthesis of 3-D porous graphite is rational, controllable, and at a low cost, which could spur a new paradigm for manufacturing an array of energy storage and conversion devices.

Materials characterizations. The morphology, microstructure, and elemental composition of the composite materials were characterized by a Hitachi S-5500 SEM equipped with STEM and energy dispersive spectroscopy detector (Bruker EDS Quantax 4010), High-Resolution TEM (JEOL 2010F), XRD (Philips automated vertical scanning general powder diffractometers), and Raman spectroscopy (Princeton instrument Inc. and Olympus IX 71). The specific surface area was measured by the Brunauer, Emmett and Teller (BET) method. All the materials were weighed by a high precision electronic balance (CAHN-C30). An electrochemistry workstation (Princeton Applied Research) was used for electrochemical deposition and characterization.

Measurements and calculations of the specific surface area. The volumetric specific surface areas of Ni foam and porous Cu—Ni foam were characterized by multi-point BET Surface Area Analysis (Pacific Surface Science Inc.). The volume specific surface areas of Ni foam and porous Cu—Ni were determined as 0.0532 m²/cm³ and 0.096 m²/cm³, respectively.

Then, the volumetric specific surface area of non-porous graphite and porous graphite can be estimated from Ni foam and porous Cu—Ni foam, respectively. Considering the Ni or Cu—Ni etching process resulted double sided (inner/outer) graphite, the volume specific surface area of porous and non-porous graphite became 0.192 m²/cm³ and 0.103 m²/cm³, respectively.

Of the same volume of 1 cm×1 cm×0.02 cm, the masses of porous and non-porous graphite/Ni(OH)₂ were measured as 0.2 mg and 0.5 mg, respectively. As a result, the specific surface area normalized by weight could be estimated as 19.2 m²/g for porous graphite/Ni(OH)₂, and 4.12 m²/g for non-porous one graphite/Ni(OH)₂. Note that the estimations shown above didn't take account of the surface area contribution from Ni(OH)₂ for either porous or non-porous graphite/Ni(OH)₂. Specific mass (mass per unit size) information of the Mn₃O₄/graphite: GMMP-30 0.37 mg/cm², GMSP-30 0.59 mg/cm², GMMP-20 0.31 mg/cm² and GMSP-20 0.48 mg/cm².

It is contemplated that any embodiment discussed in this specification can be implemented with respect to any method, kit, reagent, or composition of the invention, and vice versa. Furthermore, compositions of the invention can be used to achieve methods of the invention.

It will be understood that particular embodiments described herein are shown by way of illustration and not as limitations of the invention. The principal features of this invention can be employed in various embodiments without departing from the scope of the invention. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, numerous equivalents to the specific procedures described herein. Such equivalents are considered to be within the scope of this invention and are covered by the claims.

All publications and patent applications mentioned in the specification are indicative of the level of skill of those skilled in the art to which this invention pertains. All publications and patent applications are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.

The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.” The use of the term “or” in the claims is used to mean “and/or” unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and/or.” Throughout this application, the term “about” is used to indicate that a value includes the inherent variation of error for the device, the method being employed to determine the value, or the variation that exists among the study subjects.

As used in this specification and claim(s), the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps. In embodiments of any of the compositions and methods provided herein, “comprising” may be replaced with “consisting essentially of” or “consisting of”. As used herein, the phrase “consisting essentially of” requires the specified integer(s) or steps as well as those that do not materially affect the character or function of the claimed invention. As used herein, the term “consisting” is used to indicate the presence of the recited integer (e.g., a feature, an element, a characteristic, a property, a method/process step or a limitation) or group of integers (e.g., feature(s), element(s), characteristic(s), propertie(s), method/process steps or limitation(s)) only.

The term “or combinations thereof” as used herein refers to all permutations and combinations of the listed items preceding the term. For example, “A, B, C, or combinations thereof” is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context.

As used herein, words of approximation such as, without limitation, “about”, “substantial” or “substantially” refers to a condition that when so modified is understood to not necessarily be absolute or perfect but would be considered close enough to those of ordinary skill in the art to warrant designating the condition as being present. The extent to which the description may vary will depend on how great a change can be instituted and still have one of ordinary skilled in the art recognize the modified feature as still having the required characteristics and capabilities of the unmodified feature. In general, but subject to the preceding discussion, a numerical value herein that is modified by a word of approximation such as “about” may vary from the stated value by at least ±1, 2, 3, 4, 5, 6, 7, 10, 12 or 15%.

All of the compositions and/or methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and/or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.

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1. A method of making a three dimensional graphite structure with a controlled porosity comprising: plating a metal layer on at least one or a nickel, an iron or a cobalt foam substrate; annealing the metal and the nickel, iron or cobalt foam into a porous metal-nickel, iron or cobalt catalyst, wherein the catalyst has a smooth and a porous surface; etching the smooth surface of the annealed porous metal-nickel, iron or cobalt catalyst; growing a carbonaceous layer on the porous surface of the annealed porous metal-nickel, iron or cobalt catalyst; and etching the porous metal-nickel, iron or cobalt catalyst to obtain the graphite layer.
 2. The method of claim 1, wherein the carbonaceous layer is graphene or graphite that is deposited on the annealed porous copper-nickel catalyst by at least one of chemical vapor deposition, plasma enhanced chemical vapor deposition or sputtering. 3-4. (canceled)
 5. The method of claim 1, wherein the metal is selected from at least one of copper, nickel, iron, cobalt, gold, platinum, or rhodium, but different from the foam material.
 6. The method of claim 1, wherein the carbonaceous layer is deposited on the annealed porous copper-nickel catalyst by chemical vapor deposition in ethylene at between 600-700° C.
 7. The method of claim 1, wherein the carbonaceous layer is graphite.
 8. The method of claim 1, wherein the carbonaceous layer is freestanding and flexible.
 9. (canceled)
 10. The method of claim 1, further comprising the step of growing a metal hydroxide layer on the graphite layer.
 11. The method of claim 1, further comprising the step of growing at least one of a metal hydroxide, an oxide or a sulfide layer on the graphite layer, wherein the metal hydroxide/oxide/sulfide is selected from at least one of Ruthenium(IV) oxide; Aluminum hydroxide; Beryllium hydroxide; Cobalt(II) hydroxide; Cobalt oxide; Copper(II) hydroxide; Copper oxide; Curium hydroxide; Gold(III) hydroxide; Iron(II) hydroxide; Iron oxide; Mercury(II) hydroxide; Nickel(II) hydroxide; Nickel oxide; Nickel sulfide; Manganese oxide (MnO₂ or Mn₃O₄); Manganese sulfide; Tin(II) hydroxide; Tin(IV) Oxide; Uranyl hydroxide; Zinc hydroxide; Zirconium(IV) hydroxide; Gallium(III) hydroxide; Lead(II) hydroxide; or Thallium hydroxide.
 12. The method of claim 1, wherein the carbonaceous layer is formed into an electrode support for metal hydroxide supercapacitors. 13-16. (canceled)
 17. The method of claim 1, wherein the step of etching the porous metal-nickel, iron or cobalt catalyst is defined further as selecting an etching agent that etches the annealed porous metal-nickel, iron or cobalt.
 18. The method of claim 1, wherein the step of etching the porous metal-nickel, iron or cobalt catalyst is defined further as etching the copper-nickel catalyst in 1 M iron chloride (FeCl₃) and 2 M hydrochloride (HCl) at 50-80° C. overnight. 19-50. (canceled)
 51. A three-dimensional graphite structure comprising: a first level of pores and a second level of pores, wherein the second level of pores are smaller than the first level of pores and are disposed on the walls of said first level of pores. having different porosities
 52. The graphite structure of claim 51, wherein the graphite layer is freestanding and flexible.
 53. The graphite structure of claim 51, comprising a metal hydroxide, an oxide or a sulfide layer on the graphite.
 54. The graphite structure of claim 53, wherein the metal hydroxide, oxide, or sulfide is selected from at least one of ruthenium(IV) oxide; aluminum hydroxide; beryllium hydroxide; cobalt(II) hydroxide; cobalt oxide; copper(II) hydroxide; copper oxide; curium hydroxide; gold(II) hydroxide; iron(II) hydroxide; iron oxide; mercury(II) hydroxide; nickel(II) hydroxide; nickel oxide; nickel sulfide; manganese oxide (MnO₂ or Mn₃O₄); manganese sulfide; tin(II) hydroxide; tin(IV) Oxide; uranyl hydroxide; zinc hydroxide; zirconium(IV) hydroxide; gallium(III) hydroxide; lead(II) hydroxide; or thallium hydroxide.
 55. The graphite structure of claim 53, having a specific capacitance of at least 1149 F/g at a current density of 1.5 A/g.
 56. The graphite structure of claim 53, having at least 97.5% capacitance retention after 4,000 cycles.
 57. The graphite structure of claim 53, having at least 90% capacitance after 10,000 cycles. 